Prostate cancer is one of the most common cancer in men worldwide. Androgen receptor (AR) is a master transcription factor in driving the development and progression of the disease. Alteration in the expression or activity of AR co-factors can influence the outcome of the disease, including therapy resistance. Using a proteomics approach called rapid immunoprecipitation mass spectrometry of endogenous proteins (RIME), we identified Tripartite Motif Containing 33 (TRIM33, aka TIFlĪ³) as a novel protein interactor of AR. We show TRIM33 co-localizes with AR globally on chromatin to directly regulate genes relevant to prostate cancer progression. We demonstrate TRIM33 achieves this by stabilizing AR from ubiquitin-mediated proteasomal degradation. We also show TRIM33 is essential for prostate cancer cell growth. Finally, we found TRIM33 is upregulated in prostate cancer patients and identified a TRIM33 gene regulatory signature that can predict disease-free survival. Overall, our study has identified TRIM33 as a novel AR co-activator that enhances oncogenic AR signaling pathways in prostate cancer. These findings suggest TRIM33 may be a potential therapeutic target for prostate cancer treatment.